Sodium fluoride ignition aid in solid propellant compositions

ABSTRACT

Sodium fluoride for use as a propagation aid of combustible compositions at high altitude.

Elnited States Patent Henrich et a1.

[ SODIUM FLUORIDE IGNITION AID IN SOLID PROPELLANT COMPOSITIONS [76] Inventors: Kenneth Henrich, 60 E. Union Tpke., Wharton, NJ. 07885; Edward Costa, 41-87 St., Brooklyn, N.Y. 1 1209; Robert Wetton, Bartley Rd, Chester, NJ. 07930 (22] Filed: Mar. 11, 1968 [21] Appl. No.: 713,274

{52] US. Cl 149/18, 149/20, 149/44, 149/19.1, l49/19.9 [51] Int. Cl C06d 5/06 [58] Field of Search 149/19, 44, 19.9, 20, 18, l49/19.1

[56] References Cited UNITED STATES PATENTS 3,087.84 4/1963 Pritchard 149/19 Mar. 25, 1975 3,097,981 7/1963 Pritchard 6t 149/19 3,132,976 5/1964 Klager 6t a1. 149/19 3,156,594 11/1964 Horton 149/19 FOREIGN PATENTS OR APPLICATIONS 725,438 3/1955 United Kingdom 149/18 Primary Examiner-Benjamin R. Padgett Assistant Examiner-E. A. Miller Attorney, Agent, or Firm-Robert P. Gibson; Nathan Edelberg; Edward F. Costigan [57] ABSTRACT Sodium fluoride for use as a propagation aid of combustible compositions at high altitude.

4 Claims, N0 Drawings SODIUM FLUORIDE IGNITION AID IN SOLID PROPELLANT COMPOSITIONS This invention relates to a propagation aid for use in initiating and maintaining the combustion of a family of high energetic formulations at high altitudes. More particularly, this invention relates to the use of metallic halides as propagation aids of combustible compositions at high altitudes.

A need exists for high energetic, heat resistant compositions capable of sustained, unconfined combustions at altitudes exceeding 200,000 feet. A prime example for the application of the aforementioned compositions is in the field of rocket technology and, in par ticular, in the field of combustible rocket motor cases.

1n the past, the conventional combustible compositions of the art would not function as desired at altitudes in excess of 200,000 feet. These pyrotechnic compositions generally consisted of metallic fuels and inorganic oxidizers dispersed within a binder system.

Such formulations, however, are unable to propagate at altitudes greater than 125,000 feet. In general, they would not ignite at the altitude specified or even, if ignited, they were not capable of providing sustained, even and complete combustible activity due primarily to the low pressure under which they were to function as a result of the extremely high altitude of use.

High altitude combustion characteristics of such compositions may be improved by use of unstable oxidizers such as potassium permanganate. However, such improvements were achieved at the expense of favorable impact sensitivity and such compositions were therefore commercially unacceptable.

lt is an object to provide a propagation aid for use in the combustion of a composition containing a rubberized binder having dispersed therein a conventional metallic fuel and an oxidizer. said propagation aid functioning at altitudes in excess of 200,000 feet.

Another object is to provide a metallic halide for use in the combustion activity recited above at altitudes in excess of 200,000 feet.

Other objects and many of the attendant advantages of this invention will be further understood by reference to the following detailed description, wherein:

The metallic halides for use in this invention as propagation aids of the combustible composition include such materials as sodium fluoride and the like.

Such metallic halides should be used in an amount between about 2 and percent by weight based on the weight of the composition. In an amount below 2 percent. the desired degree of propagation of the combustible composition will not be achieved at altitudes in excess of 200,000 feet. However, a maximum degree of even propagation of the combustible composition is achieved when about 10 percent by weight of the propagation aid is utilized and little or no improvement is achieved above this amount.

The above materials may be used to greatly enhance the low pressure combustion of the formulations employing stable oxidizers, such as sodium nitrate, at altitudes in excess of 200,000 feet.

The following are typical examples of the energetic compositions into which the propagation aid may be incorporated:

Ingredients Percent by Weight Composition aluminum 27.7 sodium nitrate 52.3 sodium fluoride 10.0 .rubber binder 10.0 Composition magnesium 36.6 sodium nitrate 51.4 sodium fluoride 2.0 rubber binder 10.0

The propagation aid or metallic halide of this invention is utilized to initiate energetic compositions generally containing low molecular weight metals and inorganic oxidizers dispersed in a rubberized binder. The low molecular weight metals generally includes metals such as aluminum and magnesium and the like, while the inorganic oxidizers are generally of the more stable types such as sodium nitrate and the like. The rubberized binder serves primarily as a matrix for the dispersed materials giving strength to the compositions. Further, the above heterogeneous compositions may be shaped into the desired form by methods conventionally known in the art.

In the following example, a preferred method of incorporating the metallic halide into a combustible composition is set forth:

EXAMPLE I The metal powders, oxidizers, and propagation aids or metallic halides, all of which were initially wetted with ethyl acetate, were added in sequence to a rotating drum and rotation was continued for ten minutes. A fifteen percent ethyl acetate solution of a fluidized rubber binder was then added to the rotating drum and rotation was continued for an additional twenty minute period. The resulting slurry was then poured into the desired form and allowed to dry for twenty-four hours at room temperature. At the end of that period, the finished product was removed from the mold. Although room temperature drying was satisfactory, increased temperature would shorten the drying time. The temperature employed is, therefore, an economic choice between time and heating costs.

The metals, oxidizers and propagation aids are introduced into the drum as recited above in a fine granulated form. It has been found that the above ingredients may be used in the process in particle sizes up to and including 200 microns. However, a particle size of about 25 microns produced the most favorable results.

A complete mechanism for the interaction of the metallic halide in the combustion process is unknown. A possible explanation is that such propagation aid acts as a fluxing agent for the combustible composition or mixture. The resultant molten portion, at the base of the combustion zone, would conduct heat back into the unreacted material. This heat or activation energy for ignition is required for sustained combustion. Without this molten portion, heat transfer would be dependent upon solid state conduction and radiation. However.

heat transfer by conduction would be minimized since the material would tend to disintegrate upon combustion. Further, since reduced pressure produces an expanded flame zone. any heat transfer by radiation would vertually be eliminated.

Obviously. many modifications and variations of the present invention are possible in the light of the above techniques. It is therefore to be understood that within the scope of the appended claims. the invention may be practiced otherwise than as specifically described.

We claim:

1. An improved combustible composition of the type wherein low molecular weight metallic fuels and inorganic oxidizers are dispersed in a rubberized binder, wherein the improvement comprises: an alkali metal fluoride incorporated into said composition as a propagation aid enabling said composition to ignite and incinerate at altitudes above about 125000 feet, said al kali metal fluoride being present in an amount between about 2 and percent by weight based on the weight of said composition. 

1. AN IMPROVED COMBUSTIBLE COMPOSITION OF THE TYPE WHEREIN LOW MOLECULAR WEIGHT METALLIC FUELS AND INORGANIC OXIDIZERS ARE DISPERSED IN A RUBBERIZED BINDER, WHEREIN THE IMPROVEMENT COMPRISES: AN ALKALI METAL FLUORIDE INCORPORATED INTO SAID COMPOSITION AS A PROPAGATION AID ENABLING SAID COMPOSITION TO IGNITE AND INCINERATE AT ALTITUDES ABOVE ABOUT 125,000 FEET, SAID ALKALI METAL FLUORIDE BEING PRESENT IN AN AMOUNT BETWEEN ABOUT 2 AND 10 PERCENT BY WEIGHT BASED ON THE WEIGHT OF THE COMPOSITION.
 2. The composition of claim 1 wherein said metallic halide is sodium fluoride.
 3. The composition of claim 2 wherein said metallic fuel is magnesium and sAid sodium fluoride is present in an amount of 2 percent by weight based on the weight of said composition.
 4. The composition of claim 2 wherein said metallic fuel is aluminum and said sodium fluoride is present in an amount of 10 percent by weight based on the weight of said composition. 